The invention relates to a method for treating surfaces of substrates composed of organic or inorganic materials, in which reactive fragments, especially radicals or ions, are produced, by means of ultraviolet radiation by an ultraviolet radiator disposed at a given distance away, with a gas-filled, elongated discharge chamber whose walls are formed of a dielectric, and which is provided on the side facing away from the discharge chamber with at least one electrode, as well as an apparatus.
The method relates especially to the treatment of substrates for semiconductor technology, such as silicon substrates or glass substrates for liquid crystal displays (LCD).
In EP 0 510 503 A2 a method is disclosed for cleaning or modifying surfaces of substrates which can be in the form of fibers, fleeces, fabrics or films. To clean or modify the surfaces reactive radicals are formed by irradiating gas molecules with ultraviolet light having a wavelength between 60 and 350 nm. The radicals thus formed are made to react with the surface of the substrate. To form the radicals, molecules of oxygen, ammonia, chlorine, fluorine, hydrogen chloride, hydrogen fluoride and nitrous oxide are treated with ultraviolet radiation, and a high-power ultraviolet radiator disclosed in EP 0 254 111 A1 is to be used. The high-power radiator consists of a discharge chamber defined by a metal electrode cooled on one side and a dielectric, and filled with a noble gas or gas mixture, while both the dielectric and the other electrode lying on the surface of the dielectric facing away from the discharge chamber are transparent to the radiation produced by silent electric discharges. In this manner a large-area ultraviolet radiator of high efficiency is created, which can be operated at high electric power densities of up to 50 kW/m2 of active electrode surface.
Furthermore, DE 197 41 668 A1 discloses a discharge lamp with a tubular lamp of dielectric material defining a discharge chamber on whose surface facing away from the discharge chamber at least one electrode pair electrically insulated from one another by an insulating material is making surface-to-surface contact. The lamp tube is surrounded by an envelope tube forming an annular gap surrounding the discharge chamber, the interior of the lamp tube being divided by means of the insulating material into separate chambers insulated from one another within which the electrodes are disposed. Advantageously, the positioning of the electrodes is advantageously considerably improved as regards possible shading of the emitted light, also thereby avoiding any excessive heating of the outer wall.
In EP 0 661 110 B1 a method is disclosed for the oxidation of an object, wherein by irradiating an oxygen-containing fluid with vacuum ultraviolet radiation from a barrier discharge lamp (dielectrically hindered discharge) with encapsulated xenon gas, ozone and activated oxygen is produced by a photochemical reaction between the oxygen-containing liquid and the ultraviolet radiation; the object being treated is brought in contact with the ozone and activated oxygen and oxidized by intervention of vacuum ultraviolet radiation. According to the process the distance xe2x80x9cdxe2x80x9d of the passage of the ultraviolet radiation emitted by the barrier discharge lamp to the object is to be as short as possible and an oxygen partial pressure p (in kPa) is to be established in the area between the discharge lamp and the object according to a given algorithm.
The value given for dxc3x97p is less than 60.8, d being measured in centimeters and p in atmospheres. In this manner it is said that, in addition to an elevated oxidation rate, an improved cleaning effect is achieved by a shorter period of treatment.
It proves to be a problem that, in the state of the art, a uniform illumination of the irradiated surface is to be achieved while preserving a minimum distance between radiator and surface, and on the other hand a high radiation intensity can be sustained only at a comparatively short distance, i.e., even if an irregular radiation density is accepted.
Even if it possible to improve the uniformity of the radiation by using several radiators, a certain lack of uniformity nevertheless occurs on account of the radiator raster. Furthermore, if only a single radiator fails, the complete set of radiators has to be replaced in order to avoid irregularities due to differences in the aging processes of the radiators.
The invention sets for itself the task of setting out from the above-mentioned EP 0 510 503 A2 and applying uniformly distributed radiation of high intensity over the surface being treated, the actual radiation times being kept short by having as short a distance as possible between the radiator and the surface being treated, in order to use such radiation at low cost as an intermediate step in a production process already introduced. Furthermore, high-power radiators are to be used insofar as possible, according to the state of the art cited in the beginning.
The task is accomplished by the method, in that during the irradiation a translational and/or rotary relative movement is performed between the substrate and the ultraviolet radiator.
It proves to be especially advantageous that the intensity of a high-power radiator is so strong that it is sufficient in practice to move a single radiator, but in some cases two or more radiators, over a substrate at a comparatively slight distance without the need to increase the necessary irradiation time for one process step in an overall process.
Thus, a uniform illumination of the surface being radiated can be achieved in a simple manner.
Furthermore, it proves advantageous that the method of the invention is suitable
(a) for the cleaning of substrate surfacesxe2x80x94as for example the removal of photoresists or aerosolsxe2x80x94and for modifying the molecular surface structure by surface oxidation of the substrate with ozone and oxygen radicals under ultraviolet radiation (photons break up the surface structure), and
(b) for coating (or build-up of layers) substrate surfaces by reactive fragments out of the gas phase (between radiator and substrate surface) which settle on the surface and thus build up the coating (the photons emitted no longer interfere with coating).
In a preferred embodiment of the process, molecules of oxygen, ammonia, chlorine, fluorine, hydrochloric acid, hydrofluoric acid, hydrogen, nitrous oxide and/or silane compounds are treated with ultraviolet radiation of a wavelength between 60 nm and 350 nm, to form the radicals, and it is possible to treat individual substances or mixtures of a plurality of substances.
Preferably, an excimer radiator with a wavelength of 172 nm (xenon radiator) is used, in which case its intensity is very much stronger in comparison to ordinary radiators, resulting in a comparatively brief time of treatment with the relative movement.
Preferably, with regard to the cleavage of oxygen molecules and the formation of reactive 0(3P) and 0(1D) fragments or ozone formation, the treatment is performed under atmospheric conditions and atmospheric pressure; it is also possible, however, to perform the process in a vacuum or reduced pressure, in which case the substances being used in forming the radical molecules are placed in the area between the ultraviolet radiator and the substrate surface.
In a preferred embodiment of the invention, the discharge lamp is moved relative to the substrate along a path perpendicular to the longitudinal axis of its tubular discharge chamber, i.e., the substrate can also be moved perpendicular to the longitudinal axis of a stationary tubular discharge chamber. In this case it proves to be advantageous that a rapid coverage of a large area of the substrate is possible with a high radiation intensity through a short distance between the ultraviolet radiator and the substrate surface.
In an additional advantageous embodiment the discharge lamp is moved relative to the substrate parallel to the longitudinal axis of its tubular discharge chamber. Such irradiation is practical especially for elongated substrates or for substrates in the form of running strip material with the discharge lamp kept stationary.
In another embodiment of the invention the discharge lamp is rotated on the longitudinal axis of its discharge chamber and moved relative to the substrate; this means that one end of the elongated discharge chamber is at least approximately at the center of the rotation, while the other end moves in a direction tangential to the center point of the rotation, or, in the case of a stationary discharge lamp the substrate is moved. It is thus advantageously possible to irradiate or otherwise treat individual sectors of a substrate or a wafer as substrate in a different way.
It is furthermore possible to make a discharge lamp to rotate over the substrate surface on a rotation point in the center of the elongated discharge chamber, i.e., the substrate also can rotate under an elongated and static tubular discharge lamp. The terms, xe2x80x9crelativexe2x80x9d and xe2x80x9cabove the substrate surface, thus signifies that either the discharge lamp or the substrate is moved in translation or rotation, while the position of the discharge lamp can be arranged above or below the substrate surface being irradiated.
In a first embodiment of an apparatus for treating surfaces of substrates of organic or inorganic materials by ultraviolet irradiation with a gas-filled, elongated discharge chamber whose walls are formed by a dielectric, which is provided on the side facing away from the discharge chamber with at least one electrode, the task is solved by the invention in that at least one ultraviolet radiator is disposed in an irradiation unit wherein the apparatus has at least one displacing means for a relative translational movement between the substrate and the ultraviolet radiator.
In a preferred embodiment of the apparatus, the motion of the displacing means is produced by a controllable driver.
When such a system of relative motion between substrate and ultraviolet radiator(s) is used, considerably fewer radiators are used in comparison to the large-area radiation units of the practice, so that during operation fewer radiators need to be replaced, which ultimately also reduces the operating cost.
The task is accomplished according to the invention for a second embodiment of an apparatus for treating surfaces of substrates of organic or inorganic materials by ultraviolet radiation from an ultraviolet radiator disposed at the given distance, with a gas-filled, elongated discharge chamber whose walls are formed by a dielectric, and which is provided with at least one electrode on the side facing away from the discharge chamber, in that at least one ultraviolet radiator is disposed in an irradiation unit wherein the apparatus has at least one rotatory element for a relative rotatory movement between substrate and ultraviolet radiator.
In a preferred configuration of the second embodiment of the apparatus the rotatory element is connected to a controllable drive for the production of the rotatory movement.
In the case of relative rotatory movement between discharge lamp and substrate, it proves to be advantageous that, with a single radiator, a uniform radiation is possible in a low-cost manner; furthermore, the substrate surface can be divided into sectors of different treatment with successive steps such as, for example, cleaning, surface structuring and coating, and layered coating.
The subject matter of the invention is further explained below in conjunction with FIGS. 1, 2, 3a and 3b.